Exhaust and intake systems for industrial processes, including but not limited to spray dryers ovens, kilns etc, often include air to air energy recovery heat exchangers. The function of an industrial energy recovery heat exchanger is to transfer heat energy from the contaminated, heated exhaust of the process to the incoming fresh air supply of the process. The heat energy recovered via the transfer or exchange apparatus reduces the total fuel consumption necessary to carry out the process.
In the past, heat exchange recovery packages have usually comprised one or the other of the following typical structures. In the first type a heat exchange apparatus is mounted on a wheel which is rotated to expose the heat absorbing material first to the heated exhaust and then into the path of the incoming supply air to release the absorbed heat by contact with the cooler air.
In the second type of heat exchange recovery package, two plate fin serpentine heat exchangers are utilized, fluid is pumped through the coils to transfer heat from the exhaust side to the supply side to accomplish the heat transfer.
In another type of heat exchange recovery package commonly employed a plurality of parallel sealed individual heat exchange tubes are supported at an angle to the horizontal and contain a working fluid having both a liquid and vapor phase at the working temperatures present at the inlet and outlet portions of the apparatus. Heat transfer is accomplished by evaporation of the liquid at the hot exhaust portion of the apparatus, and condensation of the vapor at the cold intake portion with subsequent return of the condensate via capillary action and gravitational forces to the lower end of the tube. The tubes are also normally provided with fin elements bonded thereto which aid in the absorption and dissipation of heat.
Some of the problems inherent in the above identified devices are; the necessity of mechanical means to rotate the heat exchanger. in one instance and pump the fluid in another, the need for rotary seals and bearing elements, difficulty in cleaning contaminants from between the fin and tube elements, thermal expansion between the fin and tube which fractures the bond between the two elements and contaminant induced corrosion between the fin and tube which can cause a failure in the whole system or an individual tube.
Some examples of prior art heat exchange recovery systems found in the prior art are U.S. Pat. Nos.: 4,040,477, 4,064.932 and 2,529,915 which are cited merely as representative samples.